In motion dimensioning system for cuboidal objects

ABSTRACT

An in-motion measuring system for determining the length and width of linearly-moving cuboidal objects through the use of object speed, the times during which four light beams oriented across the path of the object are obstructed by the object, and the angles of the light beams with respect to the direction of object movement. The height of an object may also be determined through use of a vertically-extending light curtain with horizontally-oriented light beams, or via an ultrasonic sensor.

This is a continuation of application Ser. No. 08/496,359, filed Jun.29, 1995, now U.S. Pat. No. 5,636,028.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to ascertaining the dimensionsof three-dimensional objects and, more particularly, to determining thelength, width and height of cuboidal objects while such objects are inconstant linear motion as, for example, on a conveyor belt.

2. State of the Art

Millions of packages per year are handled and shipped by United ParcelService, Federal Express, and many other smaller courier and deliveryservices as well as by the United States Postal Service. These packagesoriginate with federal, state, and local government as well as privatebusinesses of all sizes. In many instances the charges by these carriersto their customers are based on the so-called "dim-weight" or"dimensional weight" (DW) of the object being shipped. DW is afictitious dimension based on length (L) times width (W) times height(H) in inches divided by a standard agency- or association-recognizeddivisor or dimensional weight conversion factor, commonly 166. Thus, theDW equals L×W×H divided by 166. The "166" divisor or conversion factorhas been recognized and adopted by the International Air TransportAssociation (I.A.T.A.). Even if an object or package is of an irregularconfiguration, the dim weight, using the longest measurement each oflength, width, and height, is still utilized for billing purposes. Thevolume computed by multiplication of object length times width timesheight may hereinafter be termed the "cubic volume", "spatial volume",or simply the "cube" of the object.

The measurements of the objects shipped are also critical so that thecarrier can accurately determine the number of trucks, trailers, orother vehicles which will be required to transport goods to theirdestinations and so customers and carriers can accurately estimate theirwarehousing and other storage needs.

In addition, article weight and measurements are also used to determineand predict weight and balance for transport vehicles and aircraft andto dictate the loading sequence for objects by weight and dimensions formaximum safety and efficiency.

Further, if orders of any items are to be packed into boxes, knowledgeof object weight and dimensions is useful for selecting box size anddurability.

The assignee of the present invention has been instrumental indeveloping quick, accurate means and methods for determining thedimensions and the cubic volume or spatial volume for packages and otherobjects in a commercial or industrial setting. For example, U.S. Pat.No. 5,042,015, assigned to the assignee of the present invention,discloses a practical and commercially successful means and method forobject measuring. However, the patented method and apparatus requires,for measurement of moving cuboidal objects, that the sides of theobjects be aligned parallel and perpendicular to the path of movement.Thus, there existed a need for a system for measurement of skewedcuboidal objects.

One such system for measurement of the dimensions of skewed objects (ofany shape) is described in U.S. Pat. No. 4,773,029. The system of the'029 patent, however, senses the apparent dimension of the moving objectsolely through use of infrared emitter-receiver rays and establishes thetrue length and width of an object by periodic measurements whichprovide "slices" of the object, the slices then being summed to providea horizontally planar footprint of the object from which the true lengthand width are determined. The inventors have no specific knowledge as towhether a commercial embodiment of this system in fact works asdescribed in the patent, but the system's advertised cost makes itprohibitively expensive, beyond the capabilities of many businesses, anda financial burden on those few companies able to afford it.

U.S. Pat. No. 5,105,392, assigned to the assignee of the presentinvention, provides an alternative to the system of the '029 patent formeasuring skewed cuboidal objects. The '392 patent discloses and claimsa method and an apparatus for determining the actual length and widthdimensions of a linearly moving object with a rectangular footprint bydetermining apparent length, apparent width, and the distance between anobject corner facing to the side of the travel direction and thetrailing edge of the object. These measurements are then employed todetermine the actual object length and width by trigonometrically-basedmathematical equations. The methodology as described in the '392 patenthas been proven to be sound, as have the mathematical relationships, butthe apparatus as described in the application employed to obtain thedimensions has been found lacking as to the accuracy desired by theassignee.

Yet another patent, U.S. Pat. No. 5,220,536, also assigned to theassignee of the present invention, employs a different,light-curtain-based apparatus, to determine the length and width of askewed cuboidal object and employs the mathematical relationshipspreviously developed for the '392 patent.

Another light curtain-based, in-motion dimensional measuring system isalso offered commercially by the assignee of the present invention asthe CubiScan® 200.

One problem common to all of the commercially offered in-motiondimensioning systems on the market is the necessity for a gap or "break"in the conveyor system on which the objects to be measured are moving.Thus, all of the state of the art systems for in-motion measuring ofobjects, cuboidal or otherwise, require a more or less custominstallation and must be installed in conjunction with a new conveyorsystem, or at least a segment of an existing conveyor system must bescrapped and a new system or portion with the requisite "break"installed. A further disadvantage of all commercially offered in-motiondimensioning systems is their high cost and the already-alluded-todifficulty of installation, particularly in existing warehouse,shipping, or other storage facilities which are not initially designedto accommodate these systems and in which space may be at a premium.Thus, there is a need for an accurate, relatively inexpensive, easilyinstalled dimensioning system which can be integrated not only withnewly-installed conveyor systems, but can be integrated with themajority, if not all, existing, constant-speed belt or roller typeconveyor systems.

The inventors have recognized that well in excess of 90% of all packagesand other objects which are commercially shipped in the course of normalbusiness and industry are in fact cuboidal in shape, that is to say,that such objects have a parallel top and bottom and two pairs ofmutually parallel sides, each pair of sides being at a 90° angle to theother pair and all of the sides being at a 90° angle to the top andbottom of the object (i.e., they form a parellepiped). This regular andpredictable configuration, therefore, is susceptible to a relativelysimple and inexpensive means and method developed by the inventors formeasuring length and width while the object is moving linearly at asubstantially constant rate. The height of the object may be determinedby any one of a number of approaches, including reflective ultrasound orthe use of a light curtain.

SUMMARY OF THE INVENTION

The present invention employs a system of light beams oriented to crossthe path of an object moving linearly at a known rate, so that the timethe object blocks the passage of each light beam between an emitter anda receiver can be used to determine the length and width dimensions ofthe object. The invention is specifically adapted to measure the lengthand width of cuboidal objects, as previously defined.

The apparatus of the present invention employs two pairs, or a total offour, light beams which are aimed across the path of a cuboidal objectmoving linearly and at a constant speed, such object typically beingcarried by a belt-type or roller-type conveyor as well-known in the art.There are a number of possible configurations or arrangements for thelight beam paths, but one is most preferred currently as permitting theapparatus to be relatively compact.

This preferred arrangement may be termed a "double X", wherein fouremitters are placed at one side of a linear conveyor and are aimedacross the conveyor, which carries the object toward cooperatingreceivers aimed to receive the light beams. Two of the emitters areplaced relatively close together and at an angle of 67.5° to thelongitudinal path of the conveyor means, and opposite or facing inorientation so that the first and second light beams cross to form an"X" at the center of the conveyor path. Two cooperating receivers areoriented at the same angle as the two emitters and are spaced at thesame longitudinal locations and thus at the same relative mutuallongitudinal distance as the two emitters, but on the opposite side ofthe conveyor belt. There are two additional facing emitters more widelyspaced at the same side of the conveyor as the first two emitters andoriented at an angle of 22.5° to the longitudinal path of the conveyor.Two additional receivers are placed on the opposite side of the conveyorfrom and in alignment with the latter two emitters and similarly angledat 22.5° to the conveyor path to receive the emitted light beams. Thetwo light beams from the widely-spaced emitters cross at substantiallythe same point on the conveyor path as the first two light beams fromthe closely-spaced emitters, the third and fourth light beams forming asecond "X". It is also possible to separate the two "X's" so that all ofthe beams do not intersect at a single point, or even to space each ofthe beams so that none intersect whatsoever; however, such arrangementsspread out the apparatus along the conveyor and thus are not asconvenient or compact for installation.

Another, although less preferred, arrangement of the emitter/receiverpairs considered to be practicable within a reasonable amount oflongitudinal space can be termed a "double V" configuration, whereinthere are two closely-spaced emitters at the aforementioned 67.5° angleto the path of the conveyor, and two widely-spaced emitters at theaforementioned 22.5° angle. However, unlike the first embodiment, all ofthe emitters are aimed at receivers placed at a single point on theopposite side of the conveyor. While the second embodiment may simplifyinstallation in some circumstances due to the common location for allfour receivers, the fact that the light beams do not cross but ratherconverge on a single point on the opposite side of the conveyor from theemitters of necessity renders the apparatus much longer than if acrossed-beam arrangement as in the first embodiment were employed.

Other arrangements of emitters and receivers are possible, the foregoingbeing merely convenient examples which are believed to represent thebest mode of practicing the present invention at this time. For example,it is not required that all of the emitters be placed on one side of theconveyor and all of the receivers on the other.

The basic design parameters of the invention are that a first light beambe orthogonal (at a right angle) to a second light beam in a light beampair, that the other two paired light beams be similarly orthogonal andthat the two light beam systems or pairs be rotationally skewed oroffset by a 45° angle about a vertical axis.

The dimensions of a linearly-moving object with a rectangular footprintare determined by first computing the distance the object moves alongthe conveyor while obstructing each of the four light beams, this beinga function of the rate of movement multiplied by the time the object is"in" or obstructing the beam. The projection of the object on an axisorthogonal to each beam is then computed trigonometrically, using thecosine of the angle of the beam to a line normal to the direction of theconveyor path. Four possible diagonals for the object are then computedusing the projections, and the two identical (or closest in value)diagonals are selected as representative of a rectangle. Using theprojection values associated with these two diagonals, the length andwidth of the object are then easily computed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the relationship between objecttravel through a single light beam, the linear distance moved by theobject while obstructing the beam, and the projection of the object onan axis orthogonal to the light beam corresponding to the distance ofmovement for a given angle of light beam to a line normal to thedirection of movement;

FIG. 2 is a schematic employed in an illustrative numerical example forcomputing the length and width of a cuboidal object;

FIG. 3 is a top elevation illustrating a preferred "double X" sensorarrangement for the apparatus of the present invention;

FIG. 4 is a perspective of a light beam sensor component mounted on asupporting structure at the side of a belt-type conveyor in a mannerpermitting longitudinal and rotational alignment of the sensor toaccommodate different conveyor widths; and

FIG. 5 is a sensor component and circuit macro-level schematic of apreferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Referring now to FIG. 1 of the drawings, an exemplary rectangular object50 is shown moving linearly in direction 24 at a constant rate. If l_(i)is the distance the parcel travels in beam i and φ_(i) is the acuteangle between light beam i and a normal to the direction 24 of motion,then p_(i), the projection of the parcel on axis e_(i), orthogonal tobeam i, is given by p_(i) =l_(i) cos(φ_(i)).

Since there are four light beams employed in the present invention andthus four axes e_(i), there are four projections pi and four possiblediagonals D for an object which is rectangular in the horizontal plane.If unit vectors for the four axes are: ##EQU1## Let the projections berespectively p₁, p₂, p₃, p₄. The four diagonals are determined by thefour pairs of projections on the four pairs of non-orthogonal axes. LetD₁₃ <x,y> be the diagonal determined by p_(i) and p₃. ##EQU2## Thesolution to the system with -p₁ and -p₃ is the opposite vector to thatwith +p₁ and +p₃ and represents the same diagonal so one can discard it.Similarly -p₁, +p₃ is discarded in favor of +p₁,-p₃. ##EQU3## It can beshown mathematically that the shorter of the two vectors is thediagonal, and <p₁, p₁ -√2 p₂ > is shorter, so D₁₃ =<p₁, p₁ -√2 p₃ >.

A similar analysis gives: ##EQU4## The alternate pairs of diagonals areD₁₃, D₂₄ and D₁₄, D₂₃.

So if p₁, p₂, p₃, p₄ are the projections of a rectangle, either ∥D₁₃∥=∥D₂₄ ∥ or ∥D₁₄ ∥=∥D₂₃ ∥. The equal pair D₁, D₂ are the diagonals ofthe rectangle. It can be shown mathematically that, unless the truerectangle is a square, the other pair of diagonals are of differentlengths. If the rectangle is a square, all four diagonals are the samelength. In actual application, there will be at least a smallmeasurement error and numerical error, so one does not expect trueequality. Instead, D₁ and D₂ are set to the pair whose magnitudes differleast. The length of the rectangle is the larger of 1/2∥D₁ +D₂ ∥ and1/2∥D₁ -D₂ ∥. The width is the smaller of the two.

It has been ascertained that if the two pairs of orthogonal axes e_(i)are oriented at 45° to each other and the rectangular object in questionis square, two possible squares defined by the above algorithm arecongruent, and thus the length of the side of the square can bedetermined with certainty. Further, to employ the algorithm previouslydescribed, the axes must be numbered so that their normals have the samerelative orientations as e₁ e₂, e₃, e₄.

Referring to FIG. 2 of the drawings, the following numerical example isillustrative of the methodology of the present invention, all dimensionsbeing in inches: ##EQU5## D₁₄ and D₂₃ are closest, and also agree wellwith a measured diagonal D_(m) of 10.5 of an object 50.

D₁ =<9.68, 3.91> D₂ =<-8.36, 6.19>

D₁ +D₂ =<1.32, 10.1> D₁ -D₂ =<18.04, -2.28>

1/2∥D₁ +D₂ ∥=0.5×10.19=5.09

1/2∥D₁ -D₂ ∥=0.5×18.18=9.09

So

Computed length=9.09 9.2=Measured length

Computed width=5.09 4.8=Measured width

Referring now to FIG. 3 of the drawings, an exemplary apparatus 10 ofthe present invention is schematically depicted as installed on abelt-type conveyor 100. Four light beam emitters 12, 14, 16 and 18,comprising infrared light emitting diodes, or LED's, are mounted onsupport 20, which is secured to conveyor 100 via clamping bolting offlanges 22 thereto, or is otherwise rendered stationary with respect toconveyor 100. Emitters 12 and 18 are oriented at 22.5° angles to thelinear direction of motion 24 of conveyor 100 (normals to their lightbeams being at 67.5° to the direction of motion 24), while emitters 14and 16 are oriented at 67.5° angles to the direction of motion (normalsto their light beams being at 22.5° to the direction of motion).Emitters 12 and 14 are opposite in orientation to, and facing, emitters16 and 18 at the aforementioned angles to the direction of motion 24.Light beam receivers 26, 28, 30 and 32 are placed on the opposite sideof conveyor 100 from the emitters on a similar support 20 affixed viaflanges 22 to conveyor 100. Receivers 26 and 32 are placed,respectively, opposite emitters 12 and 18 and at identical angles todirection of motion 24 as their cooperating emitters 12 and 18. Receiver32 receives a light beam from emitter 12, and receiver 26 receives alight beam from emitter 18. Receivers 28 and 30 are placed,respectively, opposite emitters 14 and 16, and at identical angles todirection of motion 24 as their cooperating emitters 14 and 16. Receiver28 receives a light beam from emitter 16, while receiver 30 receives alight beam from emitter 14. Since the light beams are constant, noexternal trigger mechanism is required to commence the timing andmeasuring sequence effected by the beams.

Timing sensors such as light beam emitter/receiver pairs 34 and 36 and38 and 40 may be aimed across conveyor 100 and perpendicular to thedirection of motion 24 to time the passage of an object over the knowndistance between the timing sensor pairs through sequential interruptionof light beams 134 and 138 by the leading edge 52 of the object 50, andthus determine the speed of the object 50. Alternatively, a contactwheel on the conveyor belt, or a rotary encoder associated with theconveyor drive, as also known in the art, may be employed to measureconveyor, and thus object, speed.

Cuboidal object 50 may be placed in any orientation on conveyor 100, sothat its passage obstructs the four light beams 112, 114, 116 and 118emitted, respectively, by emitters 12, 14, 16 and 18. In accordance withthe present invention, light beam 112 is orthogonal to and paired withlight beam 116, while light beam 114 is orthogonal to and paired withlight beam 118. The 112/116 beam pair is rotated 45° about a verticalaxis with respect to the 114/118 beam pair. As noted above, the fourdistances l₁, l₂, l₃ and l₄ the object travels while obstructing each ofthe respective light beams is, in combination with the rate of objecttravel, the basis for ascertaining the length L and width W of object50. It should be noted that the system of the present invention, in theembodiment described above, does not require any calibration to a targetobject, since conveyor speed measurement in combination with time ofinterruption of each of the four light beams avoids the need for anysuch reference.

While a reflector-type photocell system may, in theory, be usable forthe light beam aspects of the present invention, the varied orientationangles of the objects being measured, in combination with thedifferences in reflectivity of their surfaces, renders such an approachundesirable from a practical standpoint. Thus, use of through-beamphotocells, with paired infrared emitters and receivers, is thepreferred approach. Such photocell pairs are commercially available asModel No. WS/WE 6 from SICK Optic-Electronic, Inc. of Eden Prairie,Minn. The same type of paired emitters and receivers may be employed,for the sake of simplicity, for both the four light beam objectprojection sensors and the timing sensor pairs.

The receivers of each emitter/receiver pair operate on a high/lowoutput, depending upon whether the light beam from the emitter isblocked. For the sake of example only, a blocked beam may produce a highvoltage output signal (5 V), while an open or through-beam may produce alow (0 V) signal. An inverter (see FIG. 5), as known in the art, is usedto convert the 5/0 volt high/low signals to be TTL-function compatiblefor the gate circuits employed. It is desirable that the receivers havevery short transition times from light to dark and dark to light,transition time being defined as the time between breaking of a lightbeam and the resulting voltage spike at the receiver or restoration ofthe through-beam and resulting maximum voltage drop. An exemplarypreferred transition time would be less than one millisecond (<1 ms).

For enhanced accuracy and reduced interference from ambient lightsources, it is desirable to provide both emitters and receivers withvertical slit-type filters, preferably of 2 mm aperture width. Thismaximizes the spatial sensitivity of the emitter/receiver pairs andprevents light from other sources from producing false readings. It hasbeen found that a filter on both emitters and receivers is desirable.

In order to eliminate interference between light beams, beams whichcross may be spaced at different vertical levels, or emitter/receiverpairs with differing wavelengths or filtered at different wavelengthsmay be employed. It is also desirable that the light beams be co-planaror lie in parallel planes which are also parallel to the surface of theconveyor 100 so that trigonometric corrections for angles of the lightbeam plane(s) with respect to the conveyor plane are not required.

FIG. 4 depicts an exemplary sensor component 80, which may correspond toany one of emitters 12-18 or receivers 26-32, or an emitter or receiverused in a timing application. Sensor component 80 receives its supplyvoltage and sends its output through conductors of a standard cable 82to processing circuitry. Component 80 is also equipped with a mask 84defining a vertical slit 86 for passage of a light beam, and optionallyincluding a filter to block out certain wavelengths. Component 80 isshown mounted on support 20, which is affixed to conveyor system 100 viaflange 22 which is bolted as at 88 to the frame of conveyor 100. Support20 may have a slot 90 formed therein, in which slides a key 92 having arod 94 vertically extending therefrom, on which component 80 is mountedvia sensor caddy 96. Thus, as shown by arrows 102 and 104, a sensorcomponent may be moved longitudinally along conveyor 100 and rotated tothe proper angular orientation. Longitudinal adjustment is important toaccommodate differing conveyor widths, while rotational adjustmentability offers precise angular adjustment during installation. It isalso notable that the use of rod 94 permits vertical adjustment so thatthe light beams are both horizontally and vertically alignable to anoptimum extent. While not shown, it will be appreciated that means knownin the art, such as set screws, c-clamps, lock nuts, and othermechanisms may be used to secure a component 80 in its final, desiredlocation and orientation. In furtherance of ease of transport of anapparatus of the invention to its installation site, it is alsocontemplated that supports 20 may be segmented and hinged ortelescopically arranged to reduce the length of the assembly forshipping. If the width of the conveyor is known, the sensor componentsmay be pre-placed at the factory, with only fine-tuning necessary at thejob site. Installation involves only mounting the supports 20 (which mayalso be floor-mounted, if desired) and hooking sensor cables to theprocessing circuitry, which may be stand-alone or comprise a cardinserted in a PC.

The accuracy of the sensor system is dependent not only on the shorttransition times and accurate sensing of the receivers but also on theaccuracy of the time measurement of each of the four "dark" timeintervals measured for each object. Thus, use of a high speed clock isvery desirable, the speed in counts/second being ideally adjustable froma low of 10,000 per second to 1,000,000 per second, the required clockspeed for a given dimensional measurement being related to conveyorspeed.

A schematic of the sensing and processing circuitry for a preferredembodiment of the present invention is shown at FIG. 5. In FIG. 5,optical switches generally indicated at 200 and referenced as q₁, q₂, q₃and q₄ may correspond, respectively, to emitter and receiver pairs 18,26 and 14, 30 and 12, 32 and 16, 28 of FIG. 3. Optical switches q₅ andq₆ correspond to emitter and receiver pairs 34, 36 and 38, 40.Conversion to TTL signals 202 is effected by an inverter, as previouslyreferenced. The signals from optical switches q₁ -q₄ generated duringthe time said light beam is broken are counted by four of the five16-bit counters in counter array 204. The q₅ and q₆ signals aretransmitted through OR gate 206 to the remaining 16-bit counter, thesignal from q₅ starting the counter and the signal from q₆ stopping it,as the leading edge 52 of object 50 encounters the two light beams insequence.

Counter configuration and control 208 includes a clock. Counter array204 interfaces with computer or microcontroller 210 via bus interface212. Computer or microcontroller 210 controls counter array 204 throughcounter configuration and control 208. Calculation software 214 isemployed by computer or microcontroller 210 to mathematically determinethe length and width of the cuboidal object as set forth above, and theresults (and raw data, if desired) are displayed to the operator viadata display 216, which may comprise a PC monitor or other video displaydevice such as an LED numerical readout.

Computer or microcontroller 210 can interface with an external devicesuch as a host computer via external interface 218, which may comprise acard to be inserted in a host PC, the connection thereto being indicatedby connector 220. As shown, a controller with a display would beemployed for legal-for-trade applications.

While not previously discussed in any detail, it is, of course,desirable if not absolutely necessary for some applications to measurethe height of the object 50 as well as its length and width. Severalsuitable systems are available, but the preferred system is a lightcurtain system such as the BEAM-ARRAY™ system offered by BannerEngineering Corporation of Minneapolis, Minn. As shown in FIG. 3, asuitable length Model No. BME148A emitter 60 is vertically deployedabove the conveyor surface in alignment with a similar length BMR148Areceiver 62 placed across conveyor 100. Emitter 60 employs infraredlight emitting diodes (LED'S) on 0.25 inch centers, and receiver 62employs phototransistors centered on the same intervals. The LED's arefired sequentially along the length of emitter 60 at a rate of fourmilliseconds per foot of emitter length. Each emitted infrared beam isdirected to its correspondingly aligned phototransistor in receiver 62.The number of light beams broken between emitter 60 and receiver 62above the conveyor surface indicates the height of object 50.

Alternatively, a support carrying a downward-firing ultrasonic sensormay be placed over the conveyor, and the height of the object determinedfrom travel time of an ultrasonic wave reflected therefrom, in themanner disclosed in the aforementioned U.S. Pat. No. 5,042,015.

For object identification, a bar code reader such as is known in the artmay be used to read and identify each bar-coded object as it is placedon the conveyor, or as it is removed from the conveyor. It isanticipated, if the bar code is on the top or a side surface of theobject, that such reading may be automated with a reader placed over theconveyor, in combination with the measuring apparatus of the presentinvention and as a component thereof.

While the present invention has been disclosed in terms of anillustrated embodiment, those of ordinary skill in the art willrecognize that it is not so limited. Many additions, deletions andmodifications to the illustrated embodiment may be effected withoutdeparting from the scope of the invention as hereinafter claimed.

What is claimed is:
 1. An apparatus for measuring the length and widthof a linearly-moving object having a rectangular boundary traveling at adeterminable rate along a predetermined path, comprising:beam emittersfor emitting first, second, third and fourth light beams across saidpath of said linearly-moving object so as to be interrupted by thepassage thereof, each of said beam emitters being oriented to emit beamsso that each of said beams is in non-parallel orientation to each of theother three beams; a timing mechanism for determining first, second,third and fourth times during which each of said respective first,second, third and fourth light beams is interrupted by the passage ofsaid object; a speed sensing mechanism for determining magnitude of saidrate; and a processor for calculating said length and said width of saidrectangular object using said determined first, second, third and fourthtimes and a determined magnitude of said rate.
 2. The apparatus of claim1, wherein said timing mechanism for determining said times comprisesmeans for receiving each of said light beams, and a clock associatedwith said receiving means for measuring first, second, third and fourthtime intervals when said first, second, third and fourth light beams arenot received by said receiving means.
 3. The apparatus of claim 1,wherein said timing mechanism for determining the magnitude of saidsubstantially constant rate comprises:first and second timing sensorslongitudinally spaced along said path of said object at a predetermineddistance; a clock associated with said timing sensors; said first timingsensor starting said timing sensor clock responsive to passage of aleading edge of said object thereby, and said second timing sensorstopping said clock responsive to the passage of said leading objectedge thereby to establish a time interval; and means for computing saidrate magnitude from said time interval and said predetermined distance.4. The apparatus of claim 3, wherein said timing sensors comprise lightbeam sensors.
 5. The apparatus of claim 1, further including means formeasuring the height of said object.
 6. The apparatus of claim 5,wherein said means for measuring the height of said object comprises avertically extending light curtain employing horizontally-oriented lightbeams.
 7. The apparatus of claim 1, wherein said first and second lightbeams are paired in orthogonal relative orientation, said third andfourth light beams are paired in orthogonal relative orientation, andsaid first and second paired light beams are rotated 45° about an axisvertically perpendicular to said path of said linearly-moving objectwith respect to said third and fourth paired light beams.
 8. Theapparatus of claim 7, wherein said first and third light beams areoriented at a 22.5° angle to said path of said linearly-moving object,and said second and fourth light beams are oriented at a 67.5° angle tosaid path of said linearly-moving object.
 9. The apparatus of claim 8,wherein said first and third light beam emitters are aimed toward acommon point, and said second and fourth light beam emitter means areaimed toward a common point.
 10. The apparatus of claim 9, wherein saidfirst, second, third and fourth light beam emitters are placed on thesame side of said path of said linearly-moving object.
 11. The apparatusof claim 1, wherein said processor for calculating comprises amicroprocessor.
 12. The apparatus of claim 1, wherein said light beamemitters are oriented to emit said first, second, third and fourth lightbeams in one or more parallel planes parallel to the plane of movementof said linearly-moving object.
 13. The apparatus of claim 1, whereinsaid speed sensing mechanism comprises a mechanism for determining speedof a conveyor moving said object.